1. Field of the Invention
The present invention relates to a positioning device, having a pivotable shaft, to whose one end an element to be positioned can be attached, a pivot drive mechanism, a position measuring arrangement and a bearing unit, which is in particular suitable for the precise movement of a pivot arm for a servo track writer.
2. Discussion of Related Art
Such positioning devices are often employed in connection with servo track writers (STW), as mentioned above, where traces or tracks for magnetizable hard disks are installed, or written. To this end, a shaft in the STW, on which a pivot arm is fastened, is pivoted by a positioning device. A writing head is provided at the end of the pivot arm, which in the end is moved by a pivot movement of the shaft and is positioned in a highly precise manner, so that as many tracks as possible per surface unit of the hard disk can be configured. The number of tracks which are provided per surface unit or diameter unit (tracks per inch) is a measure for the storage capacity of the hard disks. For this reason continuous efforts are being made for achieving the tightest possible track formatting. An exact positioning of the pivot arms of the STW must be possible in a very short time (seek and settle time) so that the configuration of hard disks with tight track formatting can be economically provided by the producer of the hard disk.
Positioning devices are known form the publication “Servo Track Writing Technology” (Fujitsu Sci. Tech. J., 37.2, pp. 220 to 226) of December 2001, wherein the position of the pivot arm is scanned by a separate scanning unit. In this case the outlay for a relative positioning of the scanning unit in relation to the mechanical system of the pivot arm is not inconsiderable.
Further than that, positioning devices are also known, in which the scanning unit, or the entire position measuring device for measuring the angular position of the shaft to be pivoted, is placed inside a housing. So that rigid seating can be achieved, rolling bearing units are arranged at the greatest possible distance in the housing of the positioning devices of this type of construction, so that the position measuring device and the drive mechanism for moving the shaft are located between two rolling bearing units.
The known positioning devices have the disadvantage of either being constructed comparatively elaborately and not compact, and/or cannot be further improved regarding the accuracy and the seek and settle time.
Further than that, positioning devices are also known, in which the scanning unit, or the entire position measuring device for measuring the angular position of the shaft to be pivoted, is placed inside a housing. So that rigid seating can be achieved, rolling bearing units are arranged at the greatest possible distance in the housing of the positioning devices of this type of construction, so that the position measuring device and the drive mechanism for moving the shaft are located between two rolling bearing units.
The known positioning devices have the disadvantage of either being constructed comparatively elaborately and not compact, and/or cannot be further improved regarding the accuracy and the seek and settle time.
Further than that, positioning devices are also known, in which the scanning unit, or the entire position measuring device for measuring the angular position of the shaft to be pivoted, is placed inside a housing. So that rigid seating can be achieved, rolling bearing units are arranged at the greatest possible distance in the housing of the positioning devices of this type of construction, so that the position measuring device and the drive mechanism for moving the shaft are located between two rolling bearing units.
The known positioning devices have the disadvantage of either being constructed comparatively elaborately and not compact, and/or cannot be further improved regarding the accuracy and the seek and settle time.